Mortal Shell 2

Mortal Shell 2

Unreal Engine 5.6.1. Crashes on the first cutscene.

Cutscenes	61 x VP9 in .mp4, inside pakchunk0-Windows.pak and loose
Played by	Electra, decoding VP9 with its own bundled libvpx
Symptom	EXCEPTION_ACCESS_VIOLATION reading 0x0 in FElectraMediaDecoderOutputBufferPoolBlock_DX12::AllocateBuffer
Fix	Runtime patch, 4 sites, all four confirmed at runtime
CrossOver	26.3 and crossover-preview-arm64-20260821, played through on both
winevideo	Not required — see below

The fault

Electra picks its output buffer path from the graphics device:

bUseGPUBuffers = (PlatformDevice && PlatformDeviceVersion >= 12000);

On D3D12 that is true, so it takes the GPU path — and that path asks every D3D12 resource for ID3DDestructionNotifier and uses the answer without checking it got one. Apple's D3DMetal does not implement that interface, so the first VP9 frame dereferences a null vtable and the game dies.

H.264 and H.265 can avoid the buffer pool through a CVar. VPx has no equivalent, so VP9 on D3D12 has no way out through configuration.

The fix

Raise the 12000 immediate to INT_MAX in the running process. The comparison then never holds, Electra takes the CPU buffer path, and the interface it cannot get is never asked for.

The same immediate appears at four sites and all four are patched; each was confirmed to be reached at runtime rather than assumed from the disassembly.

Nothing on disk changes. The original VP9 files are left exactly as they are.

winevideo

Not required — measured. The game was played through on CrossOver 26.3 carrying no winevideo, and again on CrossOver-winevideo 26.3: the same version, differing only in the GStreamer plugins. The fix worked either way. That paired run is the controlled comparison the rest of these pages lean on, and it was made on this title and no other. crossover-preview-arm64-20260821 was measured separately, and also plays.

That matches the mechanism. VP9 never goes through Media Foundation here — Electra decodes it in-process with its own libvpx, and only the output conversion was broken, which is what the patch reroutes. The executable does import MFPlat, MFReadWrite and MF, but all three are delay-loaded, so the import table only ever said the code could reach Media Foundation, never that it did.

Install winevideo if something else needs it. This fix does not depend on it.

This title has been offered as the control for a finding that belongs to another one, and it is not one. Its 61 cutscenes are VP9 in .mp4 and it plays on stable 26.3, while DYNASTY WARRIORS: ORIGINS ships the same codec in .webm and does not — but as above, this title's VP9 never reaches CrossOver's media stack at all, so nothing it does tests what stable can open. What it is evidence for is that VP9 is not the obstacle. The container finding rests on the plugin-set comparison instead, which is in Findings, under The container, not the codec.

Caveats

• Do not use this on a game with anti-cheat. It patches a running process.
• Steam's verify integrity of game files undoes the install. No game file's contents are edited, but the game's own libogg_64.dll is moved aside and the proxy put in its place, and a verification puts the stock DLL back over it. Running install-runtime-fix.sh again restores the fix.

---

Back to the games table · Diagnosing a new game · Findings, what what they have in common